Lesson Objectives

Summarize the human population problem and possible solutions to the problem.

Vocabulary

demographic transition

changes in population that occurred in Europe and North America beginning in the 18th century, in which death rates fell and population growth rates increased, followed by birth rates falling and population growth rates decreasing

Introduction

Humans have been called the most successful “weed species” Earth has ever seen. Like weeds, human populations are fast growing. They also disperse rapidly. They have colonized habitats from pole to pole. Overall, the human population has had a pattern of exponential growth, as shown in Figurebelow. The population increased very slowly at first. As it increased in size, so did its rate of growth.

Growth of the Human Population. This graph gives an overview of human population growth since 10,000 BC. It took until about 1800 AD for the number of humans to reach 1 billion. It took only a little over 100 years for the number to reach 2 billion. Today, the human population is rapidly approaching the 7 billion mark! Why do you think the human population began growing so fast?

Early Population Growth

Homo sapiens arose about 200,000 years ago in Africa. Early humans lived in small populations of nomadic hunters and gatherers. They first left Africa about 40,000 years ago. They soon moved throughout Europe, Asia, and Australia. By 10,000 years ago, they had reached the Americas. During this long period, birth and death rates were both fairly high. As a result, population growth was slow. Humans invented agriculture about 10,000 years ago. This provided a bigger, more dependable food supply. It also let them settle down in villages and cities for the first time. The death rate increased because of diseases associated with domestic animals and crowded living conditions. The birth rate increased because there was more food and settled life offered other advantages. The combined effect was continued slow population growth.

Demographic Transition

Major changes in the human population first began during the 1700s in Europe and North America. First death rates fell, followed somewhat later by birth rates.

Death Rates Fall

Several advances in science and technology led to lower death rates in 18th century Europe and North America:

New scientific knowledge of the causes of disease led to improved water supplies, sewers, and personal hygiene.

Better farming techniques and machines increased the food supply.

The Industrial Revolution of the 1800s led to new sources of energy, such as coal and electricity. This increased the efficiency of the new agricultural machines. It also led to train transport, which improved the distribution of food.

For all these reasons, death rates fell, especially in children. This allowed many more children to survive to adulthood, so birth rates increased. As the gap between birth and death rates widened, the human population grew faster.

Birth Rates Fall

It wasn’t long before birth rates started to fall as well in Europe and North America. People started having fewer children because large families were no longer beneficial for several reasons.

As child death rates fell and machines did more work, farming families no longer needed to have as many children to work in the fields.

Laws were passed that required children to go to school. Therefore, they could no longer work and contribute to their own support. They became a drain on the family’s income.

Eventually, birth rates fell to match death rates. As a result, population growth slowed to nearly zero.

Stages of the Demographic Transition

These changes in population that occurred in Europe and North America have been called the demographic transition. The transition can be summarized in the following four stages, which are illustrated in Figurebelow:

Stage 1—High birth and death rates lead to slow population growth.

Stage 2—The death rate falls but the birth rate remains high, leading to faster population growth.

Stage 3—The birth rate starts to fall, so population growth starts to slow.

Stage 4—The birth rate reaches the same low level as the death rate, so population growth slows to zero.

Stages of the Demographic Transition. In the demographic transition, the death rate falls first. After a lag, the birth rate also falls. How do these changes affect the rate of population growth over time?

Recent Population Growth

At one time, scientists predicted that all human populations would pass through the same demographic transition as Europe and North America. Now, they are not so sure. Death rates have fallen throughout the world. No country today remains in Stage 1 of the transition. However, birth rates are still high in many poor countries. These populations seem to be stuck in Stage 2. An example is the African country of Angola. Its population pyramid for 2005 is shown in Figurebelow. The wide base of the pyramid base reflects the high birth rate of this population.

Angola’s population pyramid is typical of Stage 2 of the demographic transition.

Many other countries have shifted to Stage 3 of the transition. Birth rates have started to fall. As a result, population growth is slowing. An example is Mexico. Its population pyramid for 1998 is shown in Figurebelow. It reflects a recent fall in the birth rate.

Mexico’s 1998 population pyramid is typical of Stage 3 population. How can you tell that the birth rate has started to fall?

Most developed nations have entered Stage 4. Sweden is an example (see Figurebelow). The birth rate has been low for many years in Sweden. Therefore, the rate of population growth is near zero.

Sweden’s 1998 population pyramid shows a population in Stage 4.

In some countries, birth rates have fallen even lower than death rates. As result, their population growth rates are negative. In other words, the populations are shrinking in size. These populations have top-heavy population pyramids, like the one for Italy shown in Figurebelow. This is a new stage of the demographic transition, referred to as Stage 5. You might think that a negative growth rate would be a good thing. In fact, it may cause problems. For example, growth-dependent industries decline. Supporting the large aging population is also a burden for the shrinking younger population of workers.

This 1998 population pyramid for Italy represents a Stage 5 population.

Future Population Growth

The human population is now growing by more than 200,000 people a day. At this rate, there will be more than 9 billion people by 2050. The human population may well be close to its carrying capacity. It has already harmed the environment. An even larger human population may cause severe environmental problems. This could lead to outbreaks of disease, starvation, and global conflict. There are three potential solutions:

Use technology to make better use of resources to support more people.

India will be the most populous nation, surpassing China sometime around 2025.

The U.S. will remain the third most populous nation, with a population of 423 million (up from 308 million in 2010).

Declining birth rates Japan and Russia will cause them to fall from their current positions as the 9th and 10th most populous nations, respectively, to 16th and 17th.

Nigeria will have a population of 402 million, up from 166 million people.

Ethiopia's population will likely triple, from 91 million to 278 million, making the East African nation one of the top 10 most populous countries in the world.

So what does all this mean?

The African continent is expected to experience significant population growth in the coming decades, which could compound the already-problematic food-supply issues in some African nations.

Immigration and differing birth rates among races will change the ethnic composition of the U.S.

Population booms in Africa and India, the decline of Russia and the expected plateau of China will all change the makeup of the estimated 9.4 billion people who will call Earth home in 2050.

Lesson Summary

Early humans lived in small populations of nomadic hunters and gatherers. Both birth and death rates were fairly high. As a result, human population growth was very slow. The invention of agriculture increased both birth and death rates. The population continued to grow slowly.

Major changes in the human population first began during the 1700s. This occurred in Europe and North America. First, death rates fell while birth rates remained high. This led to rapid population growth. Later, birth rates also fell. As a result, population growth slowed.

Other countries have completed a similar demographic transition. However, some countries seem stalled at early stages. They have high birth rates and rapidly growing populations.

The total human population may have to stop growing eventually. Even if we reduce our use of resources and distribute them more fairly, at some point the carrying capacity will be reached.

Lesson Review Questions

Recall

1. How did the invention of agriculture affect human birth and death rates? How did it affect human population growth?

2. Outline the four stages of the demographic transition as it occurred in Europe and North America.

3. State two reasons why death rates fell in Europe and North America, starting in the 1700s.

4. Why did birth rates fall in Europe and North America during the demographic transition?

5. Why was a fifth stage added to the demographic transition model? Describe a population at this stage.

Apply Concepts

6. Which stage of the demographic transition is represented by the population pyramid below?

7. Assume you will add a line to the graph in Figureabove to represent the population growth rate (r). Describe what the line would like.

Think Critically

8. Evaluate how well the original demographic transition model represents human populations today.

9. What is the human population problem? What are some potential solutions? Which solution do you think is best? Present a logical argument to support your choice.

Points to Consider

The human population may already be larger than its carrying capacity.

What evidence might show that there are too many people on Earth today?

How does human overpopulation affect the environment? How does it affect the populations of other species?